Cold energy recovery process based on natural gas supersonic spray pipe decarburization

Abstract

The invention relates to a cold energy recovery process based on natural gas supersonic spray pipe decarburization. The system comprises a decarburization unit, a cold energy recovery unit, a CO2 conveying unit and a cold energy storage unit. The decarburization unit comprises a Laval nozzle and a gas cyclone; the cold energy recovery unit comprises a micro-channel heat exchanger and a supercritical CO2 double-layer vacuum heat insulation conveying pipeline; the CO2 conveying unit comprises a compressor and a cooler; the cooling capacity storage unit comprises a throttling valve, a low-temperature storage tank and a booster pump. According to the technology, the technical scheme of supersonic velocity spray pipe decarburization and CO2 working medium phase change energy storage is adopted, low-temperature natural gas at an outlet of a supersonic velocity spray pipe is used for conducting heat exchange with a CO2 working medium, CO2 which absorbs cold energy and is liquefied is stored in a low-temperature storage tank, and recovery of excessive cold energy can be achieved while natural gas temperature returning is achieved. Compared with the prior art, the system has the advantages of being high in cold energy recovery rate, low in system energy consumption, high in equipment integration degree, large in cold storage density, free of secondary pollution and the like, efficient recovery and long-term storage of cold energy in the decarburization process can be achieved, and an innovative solution is provided for comprehensive utilization of cold energy in the field of industrial tail gas decarburization.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy recovery, relates to natural gas decarbonization and cold energy recovery, and particularly relates to a cold energy recovery process based on natural gas supersonic nozzle decarbonization. Background Art

[0002] Natural gas often contains a certain amount of CO2. During subsequent liquefaction, it will not only increase the liquefaction energy consumption and exacerbate equipment corrosion, but also form dry ice to block pipelines during low-temperature liquefaction, threatening production safety. Traditional decarbonization technologies such as amine liquid absorption method have high energy consumption and large equipment, while the membrane separation method, although compact, is easily affected by high pressure and impurities, resulting in efficiency attenuation, and it is difficult to adapt to harsh working conditions such as offshore floating LNG (FLNG) or distributed gas fields. The supersonic nozzle decarbonization technology forms a shock wave quenching effect through the supersonic expansion of gas, making CO2 condense into liquid particles at low temperature and low pressure, so as to achieve efficient separation and be captured by a cyclone separator. This technology combines the advantages of low-temperature separation and pressure energy recovery, does not require chemical reagents, and has a compact structure. It is particularly suitable for the treatment of unconventional gas sources with high pressure and high CO2 content, can reduce the pre-treatment energy consumption before liquefaction, and simultaneously recover liquid CO2 for oil displacement and storage or industrial raw materials, meeting the requirements of energy consumption reduction and efficiency improvement in the entire LNG industrial chain under the "dual carbon" goal, and providing key technical support for building a green and low-carbon energy system.

[0003] Driven by the global "dual carbon" goal, carbon capture, utilization, and storage (CCUS) technology has become the core path to achieve carbon neutrality. In recent years, data from the International Energy Agency (IEA) shows that the number of global CCUS projects has increased by more than 30% annually on average. The CO2 utilization mode has transformed from single sequestration to diversified resource utilization, such as enhanced oil recovery, synthetic fuels, microalgae carbon sequestration, and cold energy recovery, etc., and its economic and environmental benefits have been significantly improved. China has clearly listed CCUS as a key area for low-carbon technology research, aiming to promote the transformation of CO2 from a "waste" to a dual-attribute "industrial raw material + energy carrier", and innovative technologies are needed to achieve deep coupling in the capture and utilization links. Meanwhile, in the natural gas liquefaction (LNG) industrial chain, the demand for decarbonizing the feed gas is urgent. Simply using the traditional amine process has high energy consumption and the chemical reagents are highly polluting. Against this background, the miniaturized supersonic nozzle decarbonization technology has attracted much attention due to its compact and efficient characteristics. However, the natural gas after decarbonization by the supersonic nozzle has excess cold energy, which hinders its subsequent normal-temperature treatment. Simply heating the natural gas will waste the cold energy and increase the equipment energy consumption. Therefore, it is crucial to recover the excess cold energy in the natural gas. Compared with other cold energy recovery working fluids, the CO2 captured during oil and gas field development absorbs the excess cold energy generated during the decarbonization process of the supersonic nozzle through a heat exchange process and then liquefies. It is recovered and stored together with the liquid CO2 condensed in the nozzle and used for enhanced oil recovery or chemical synthesis, etc., thus constructing a "decarbonization - cold energy recovery - carbon utilization" closed loop and achieving "carbon treatment with carbon". This process provides an integrated solution for the low-carbon transformation of the energy industry.

[0004] When dealing with the problem of subcooled natural gas after decarbonization by the supersonic nozzle, simply heating the natural gas not only incurs the energy consumption required for the heating equipment but also wastes the excess cold energy in the supersonic nozzle. This violates the principles of energy conservation and maximization of resource utilization. Due to physical property limitations, existing heat exchange working fluids are difficult to simultaneously meet the requirements of high-density storage, multi-scenario reuse, and negative carbon emissions. The technical solution of using the captured CO2 as the heat exchange working fluid in this invention replaces the traditional heating method to deal with the problem of subcooled natural gas, converting it into a directly utilizable liquid resource. It can not only save the high energy consumption required for directly heating natural gas and reduce the investment cost of the CO2 liquefaction process but also has a higher cold energy storage density and more flexible applicability. It has the advantages of high cold energy storage density, flexible resource utilization mode, low CO2 liquefaction energy consumption and process complexity, low equipment investment, and good environmental benefits. Therefore, a cold energy recovery process based on the decarbonization of natural gas by a supersonic nozzle is established. Summary of the Invention

[0005] Aiming at the problems of waste of excess cold energy in the existing supersonic nozzle decarbonization process and high energy consumption and relatively complex equipment in the CO2 liquefaction process, the purpose of the present invention is to provide a cold energy recovery process based on natural gas supersonic nozzle decarbonization. This process adopts the technical solution of supersonic nozzle decarbonization + CO2 working medium phase change energy storage, which can simultaneously carry out natural gas temperature recovery and CO2 liquefaction. Compared with other processes under the same conditions, this process has the advantages of high cold energy storage density, flexible resource utilization method, low CO2 liquefaction energy consumption and process complexity, less equipment investment, and good environmental protection benefits.

[0006] To achieve the above object, the present invention provides a cold energy recovery process based on natural gas supersonic nozzle decarbonization, including a decarbonization unit (cold energy production unit), a cold energy recovery unit, a CO2 transportation unit, and a cold energy storage unit;

[0007] The decarbonization unit includes a Laval nozzle and a gas cyclone; the cold energy recovery unit includes a microchannel heat exchanger HX-1 and a supercritical CO2 double-layer vacuum adiabatic transportation pipeline; the CO2 transportation unit includes a compressor K-1, a cooler E-1, and a supercritical CO2 double-layer vacuum adiabatic transportation pipeline; the cold energy storage unit includes a throttle valve V-1, a throttle valve V-2, a low-temperature storage tank T-1, and a booster pump P-1;

[0008] In the decarbonization unit, the raw gas inlet pipeline is connected to the supersonic nozzle N-1; the decarbonized natural gas flows out from the end of the supersonic nozzle N-1.

[0009] In the cold energy recovery unit, the microchannel heat exchanger inlet, the microchannel heat exchanger HX-1, and the microchannel heat exchanger outlet are connected in sequence.

[0010] In the CO2 transportation unit, the supercritical CO2 double-layer vacuum adiabatic transportation pipeline, the compressor K-1, and the cooler E-1 are connected in sequence, and the CO2 is controlled at 7.38 MPa and 31 °C (supercritical state) through the compressor K-1 and the cooler E-1.

[0011] In the cold energy storage unit, the microchannel heat exchanger outlet and the annular liquid collecting cavity are connected to the throttle valve V-1, and the throttle valve V-1, the low-temperature storage tank T-1, the throttle valve V-2, and the booster pump P-1.

[0012] For the above cold energy recovery process based on natural gas supersonic nozzle decarbonization, the raw gas can be natural gas at normal temperature and any pressure, and the applicable range of raw gas conditions is relatively wide.

[0013] The above cold energy recovery process based on the decarbonization of a natural gas supersonic nozzle. The supersonic nozzle N-1 mainly realizes the processes of isentropic expansion (temperature and pressure reduction), CO2 condensation (non-equilibrium phase change), and gas-liquid separation of natural gas in this device. In the present invention, an inlet swirl section, a supersonic expansion section, a nucleation condensation section, and a gas-liquid separation section are provided inside the supersonic nozzle N-1;

[0014] The inlet swirl section is provided with spiral guide vanes (angle 20° - 30°), which cause the natural gas to generate high-speed swirl. The diameter of the swirl chamber gradually decreases and smoothly transitions to the throat of the subsequent nozzle. A strong centrifugal force field is generated through the swirl to pre-separate part of the liquid CO2 (fling the liquid towards the wall surface), and at the same time provide a uniform flow field for the subsequent expansion section;

[0015] The supersonic expansion section is provided with a Laval nozzle. The contraction section accelerates the airflow to the sonic speed at the throat, and the expansion section further accelerates it to supersonic speed; the temperature of the airflow drops rapidly to -30°C to -60°C through adiabatic expansion, and the pressure drops to 0.5 to 2 bar, creating a low-temperature and low-pressure environment for CO2 condensation;

[0016] The nucleation condensation section is provided with a non-equilibrium condensation region. In this region, due to the relatively high dew point temperature of CO2, it rapidly becomes supersaturated at low temperatures and preferentially nucleates and grows into droplets on the wall surface;

[0017] The gas-liquid separation section is provided with an annular liquid collection chamber. The annular liquid collection chamber is isolated from the central gas channel. The preferentially condensed liquid CO2 is flung towards the wall surface by the centrifugal force generated by the cyclone and discharged through the liquid collection chamber; the decarbonized natural gas is output from the central channel.

[0018] The above cold energy recovery process based on the decarbonization of a natural gas supersonic nozzle. The heat exchanger includes a microchannel heat exchanger HX-1, whose main function is to achieve heat exchange and transfer during the production of this device. It is a heat exchange device in the field with the characteristics of small volume and high heat transfer rate. In the present invention, a spiral micro heat exchange channel is provided in the heat exchanger HX-1;

[0019] The end of the spiral micro heat exchange channel is connected to the throttle valve V-1 through a double-layer vacuum adiabatic transmission pipeline, and the beginning of the spiral micro heat exchange channel is connected to the cooler E-1 through a double-layer vacuum adiabatic transmission pipeline;

[0020] The above cold energy recovery process based on the decarbonization of a natural gas supersonic nozzle is composed of a compressor K-1, a cooler E-1, the spiral micro heat exchange channel in the microchannel heat exchanger HX-1, a double-layer vacuum adiabatic transmission pipeline, and the connecting pipelines between adjacent components to jointly form a liquid CO2 production path.

[0021] In the above cold energy recovery process for decarbonization based on a natural gas supersonic nozzle, the expanded low-temperature natural gas in the decarbonization unit (cold energy production unit) directly provides cold energy for CO2, causing it to liquefy.

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] (1) In the cold energy recovery process for decarbonization based on a natural gas supersonic nozzle provided by the present invention, natural gas decarbonization and CO2 liquefaction are respectively carried out through a supersonic nozzle and a microchannel heat exchanger. Based on the traditional CO2 liquefaction process, the present invention enables the simultaneous progress of natural gas decarbonization and CO2 liquefaction. The combination of the two processes reduces the investment in equipment and refrigerants. While decarbonizing natural gas, it can efficiently achieve CO2 liquefaction without the need for refrigerants, realizing the reduction of additional energy consumption for CO2 liquefaction and the full utilization of the excess cold energy in natural gas.

[0024] (2) In the cold energy recovery process for decarbonization based on a natural gas supersonic nozzle provided by the present invention, the cold energy recovery unit uses CO2 as the cold energy recovery medium, which can either be sourced from the CO2 captured in oil and gas fields or be utilized in multiple aspects for the liquefied CO2. It has the advantages of low device complexity, low investment, and high cold energy storage density, realizing the transformation of CO2 from waste to resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the process flow diagram of the cold energy recovery process for decarbonization based on a natural gas supersonic nozzle of the present invention;

[0026] Figure 2 is the schematic diagram of microchannel heat transfer in the supersonic nozzle of the present invention;

[0027] Figure 3 is the cross-sectional view of the microchannel heat exchanger in the supersonic nozzle of the present invention;

[0028] Description of the reference numerals: N-1 - supersonic nozzle; V-1 - throttle valve; V-2 - throttle valve; K-1 - compressor; E-1 - cooler; HX-1 - microchannel heat exchanger; T-1 - low-temperature storage tank; P-1 - booster pump. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following will combine with the attached Figure 1 、attached Figure 2 、attached Figure 3 to clearly and completely describe the technical solution of the cold energy recovery process for decarbonization based on a natural gas supersonic nozzle provided by the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention.

[0030] A cold energy recovery process for decarbonization based on a natural gas supersonic nozzle provided in this embodiment is asFigure 1 As shown, it includes a decarbonization unit (cold energy production unit), a cold energy recovery unit, a CO2 transportation unit, and a cold energy storage unit connected by pipelines.

[0031] The decarbonization unit includes a gas cyclone, a Laval nozzle, and an annular liquid collection chamber;

[0032] The cold energy recovery unit includes a microchannel heat exchanger and a supercritical CO2 double-layer vacuum adiabatic transportation pipeline;

[0033] The CO2 transportation unit includes a compressor K-1, a cooler E-1, and a supercritical CO2 double-layer vacuum adiabatic transportation pipeline. The CO2 is controlled at 7.38 MPa and 31 °C (supercritical state) through the compressor K-1 and the cooler E-1.

[0034] The cold energy storage unit includes a throttle valve V-1, a throttle valve V-2, a low-temperature storage tank T-1, and a booster pump P-1.

[0035] The end of the spiral microchannel heat exchanger is connected to the throttle valve V-1 through a double-layer vacuum adiabatic transportation pipeline, and the beginning of the spiral microchannel heat exchanger is connected to the cooler E-1 through a double-layer vacuum adiabatic transportation pipeline;

[0036] The above cold energy recovery process based on natural gas supersonic nozzle decarbonization is composed of a compressor K-1, a cooler E-1, a spiral microchannel in the microchannel heat exchanger HX-1, a double-layer vacuum adiabatic transportation pipeline, and the connecting pipelines between adjacent components to jointly form a liquid CO2 production path.

[0037] In the above cold energy recovery process based on natural gas supersonic nozzle decarbonization, the expanded low-temperature natural gas in the decarbonization unit (cold energy production unit) directly provides cold energy for CO2 to liquefy it.

[0038] In the above cold energy recovery process based on natural gas supersonic nozzle decarbonization, the raw material gas can be natural gas at normal temperature and any pressure, and the applicable range of raw material gas conditions is relatively wide.

[0039] A cold energy recovery process based on natural gas supersonic nozzle decarbonization provided in this embodiment, as Figure 2 、 Figure 3 shown, includes an inlet swirl section, a supersonic expansion section, a nucleation condensation section, a gas-liquid swirl separation section, and a cold energy recovery section.

[0040] In the above natural gas liquefaction process using a supersonic nozzle for precooling, there is a supersonic nozzle N-1, whose main function is to achieve the processes of isentropic expansion (temperature and pressure reduction) of the gas, CO2 condensation (non-equilibrium phase change), and gas-liquid separation in this device. In the present invention, an inlet swirl section, a supersonic expansion section, a nucleation condensation section, a gas-liquid separation section, and a cold energy recovery section are provided inside the supersonic nozzle N-1;

[0041] The inlet swirl section is provided with spiral guide vanes (angle 20° - 40°), which force natural gas to form a high-speed swirl. The diameter of the swirl chamber gradually decreases and smoothly transitions to the throat of the subsequent nozzle to avoid flow separation. A strong centrifugal force field is generated by the swirl, causing the gas to swirl into the throat of the nozzle and at the same time providing a uniform flow field for the subsequent expansion section;

[0042] The supersonic expansion section is provided with a Laval nozzle. The converging section accelerates the airflow to the sonic speed at the throat, and the diverging section further accelerates it to supersonic speed; the temperature of the airflow drops sharply to -30°C to -60°C and the pressure drops to 0.5 - 2 bar through adiabatic expansion, creating a low-temperature and low-pressure environment for CO2 condensation;

[0043] The nucleation and condensation section is provided with a non-equilibrium condensation zone. In this zone, CO2 has a relatively high dew point temperature and rapidly becomes supersaturated at low temperatures, preferentially nucleating and growing into droplets on the wall surface;

[0044] The gas-liquid separation section is provided with an annular liquid collection chamber, which is isolated from the central gas channel. The preferentially condensed liquid CO2 is thrown towards the wall surface by the centrifugal force generated by the cyclone and discharged through the liquid collection chamber; the decarbonized natural gas is output from the central channel.

[0045] The cold energy recovery section is provided with a microchannel heat exchanger. The heat exchange channels in the microchannel heat exchanger are spirally embedded in the channel grooves engraved on the inner wall at the end of the supersonic nozzle. The width of the heat exchange channels is 50 - 200 μm, and the inclination direction of the heat exchange channels forms an angle of 30° - 50° with the horizontal. The heat exchange medium CO2 enters the heat exchange microchannels through the pipeline and exchanges heat with the low-temperature natural gas at the end of the supersonic nozzle, absorbing the excess cold energy in the natural gas and liquefying. The color of the CO2 flow in the heat exchange channels gradually changes to indicate its temperature drop (red represents the hot flow and blue represents the cold flow).

[0046] The above is to help readers understand the principle of the present invention. The protection scope of the present invention is not limited to such specific statements and embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several combinations and improvements can be made, and these combinations and improvements are also within the protection scope of the present invention.

Claims

1. A cold energy recovery process based on decarbonization of a natural gas supersonic nozzle, characterized in that: It includes a decarbonization unit (cold production unit), a cold energy recovery unit, a CO2 transportation unit, and a cold energy storage unit; The decarbonization unit includes a Laval nozzle and a gas cyclone; the cold energy recovery unit includes a microchannel heat exchanger HX-1 and a supercritical CO2 double-layer vacuum adiabatic transportation pipeline; the CO2 transportation unit includes a compressor K-1 and a cooler E-1; the cold energy storage unit includes a throttle valve V-1, a throttle valve V-2, a low-temperature storage tank T-1, and a booster pump P-1; For the decarbonization unit, the raw gas inlet pipeline is connected to the supersonic nozzle N-1; the decarbonized natural gas flows out from the end of the supersonic nozzle N-1; For the cold energy recovery unit, the microchannel heat exchanger inlet, the microchannel heat exchanger HX-1, and the microchannel heat exchanger outlet are connected in sequence; For the CO2 transportation unit, the CO2 transportation pipeline, the compressor K-1, and the cooler E-1 are connected in sequence; For the cold energy storage unit, the microchannel heat exchanger outlet and the annular liquid collection chamber are connected to the throttle valve V-1, and the throttle valve V-1, the low-temperature storage tank T-1, the throttle valve V-2, and the booster pump P-1.

2. The cold energy recovery process based on decarbonization of a natural gas supersonic nozzle according to claim 1, wherein: The microchannel heat exchanger HX- is provided with a spiral micro heat exchange channel. The end of the spiral micro heat exchange channel is connected to the throttle valve V-1 through a double-layer vacuum adiabatic transportation pipeline, and the beginning of the spiral micro heat exchange channel is connected to the cooler E-1 through a pipeline; 3. A cold energy recovery method based on decarbonization of a natural gas supersonic nozzle, characterized in that: It includes an inlet swirl section, a supersonic expansion section, a nucleation condensation section, a gas-liquid separation section, and a cold energy recovery section; The inlet swirl section is provided with spiral guide vanes (angle 20° - 40°), which force the natural gas to form a high-speed swirl. The diameter of the swirl chamber gradually decreases and smoothly transitions to the throat of the subsequent nozzle to avoid flow separation. A strong centrifugal force field is generated through the swirl, causing the gas swirl to enter the throat of the nozzle and providing a uniform flow field for the subsequent expansion section at the same time; The supersonic expansion section is provided with a Laval nozzle. The converging section accelerates the airflow to the speed of sound at the throat, and the diverging section further accelerates it to supersonic speed; through adiabatic expansion, the temperature of the airflow drops suddenly to -30°C to -60°C, and the pressure drops to 0.5 - 2 bar, creating a low-temperature and low-pressure environment for CO2 condensation; The nucleation condensation section is provided with a non-equilibrium condensation zone. In this zone, CO2 has a relatively high dew point temperature and becomes rapidly supersaturated at low temperatures, preferentially nucleating and growing into droplets on the wall surface; The gas-liquid separation section is provided with an annular liquid collection chamber. The annular liquid collection chamber is isolated from the central gas channel. The preferentially condensed liquid CO2 is thrown towards the wall surface by the centrifugal force generated by the cyclone and discharged through the liquid collection chamber; the decarbonized natural gas is output from the central channel. The cold energy recovery section is provided with a microchannel heat exchanger. The heat exchange channels in the microchannel heat exchanger are spirally embedded in the channel grooves engraved on the inner wall at the end of the supersonic nozzle. The width of the heat exchange channels is 50 - 200 μm, and the inclination direction of the heat exchange channels forms an angle of 30° - 50° with the horizontal. The heat exchange medium CO2 enters the heat exchange microchannels through the pipeline and exchanges heat with the low-temperature natural gas at the end of the supersonic nozzle, absorbing the excess cold energy in the natural gas and liquefying. The color of the CO2 stream in the heat exchange channels gradually changes to indicate its temperature drop (red represents the hot stream, and blue represents the cold stream).

4. The cold energy recovery process based on decarbonization of natural gas supersonic nozzle according to any one of claims 1-3, characterized in that: The natural gas decarbonization system directly provides cooling capacity for CO2 through the microchannel heat exchanger in the supersonic nozzle; the double-layer vacuum adiabatic pipeline provides the transportation conditions for the liquefied CO2; CO2 is used as the working medium for cold energy recovery and storage.

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